1. Field of the Invention
The present invention relates to a fuel cell system capable of unsealing a cathode of a fuel cell before scavenging flowpaths in the fuel cell, in which electro-chemical reaction has been stopped previously by closing a first shut-off valve and a second shut-off valve.
2. Description of the Related Art
Japanese Patent Laid-open Publication No. 2008-218072 (hereinafter called Patent Document 1) discloses an example of fuel cell system having fuel cells including an air-inlet shut-off valve provided at an inlet of a cathode and an air-outlet shut-off valve provided at an outlet of the cathode and preventing gas cross-leak, i.e. a short circuit caused by either gas passing from one side to the other side of the fuel cell through a membrane while no electro-chemical reaction is under way in the fuel cell, by sealing the cathode by means of the air-inlet shut-off valve and the air-outlet shut-off valve after stopping the electro-chemical reaction from progressing in the fuel cell.
The fuel cell system disclosed in Patent Document 1 has a buffer tank for storing air compressed by an air compressor. The pressure of air stored in the buffer tank is higher than a pressure of air supplied to the fuel cell. The fuel cell system disclosed in Patent Document 1 switches the air-inlet shut-off valve and the air-outlet shut-off valve to open and close by using a pressure difference between an atmospheric pressure chamber communicating with ambient air and a pressurized chamber containing the air supplied from the buffer tank.
Japanese Patent Laid-open Publication No. 2006-221836 (hereinafter called Patent Document 2) discloses a fuel cell system including a fuel cell. The fuel cell system disclosed in Patent Document 2 has two normally-closed electromagnetic valves provided respectively at an outlet and an inlet of a cathode, and closes the electromagnetic valves while no electro-chemical reaction is under way in the fuel cell.
The fuel cell systems disclosed in Patent Documents 1 and 2 cannot be restarted sometimes if water remaining on seat sections and on valve bodies pressed against the seat sections freezes in the shut-off valves when ambient temperature lowers below the freezing temperature after stopping electro-chemical reaction in these prior art fuel cells and sealing the cathode by using shut-off valves.